The isotopic signature of monsoon conditions,cloud modes,and rainfall type          下载免费PDF全文

Costijn Zwart  Niels C. Munksgaard  Alain Protat  Naoyuki Kurita  Dionisia Lambrinidis  Michael I. Bird 《水文研究》2018,32(15):2296-2303

This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ¹⁸O and δ²H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes.  相似文献   

Small hypervelocity particles captured in aerogel collectors: Location,extraction, handling and storage     

Andrew J. Westphal  Christopher Snead  Janet Borg  Eric Quirico  Pierre‐Ivan Raynal  Michael E. Zolensky  Gianluca Ferrini  Luigi Colangeli  Pasquale Palumbo 《Meteoritics & planetary science》2002,37(6):855-865

Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit.  相似文献   

Accuracy assessment of digital elevation models by means of robust statistical methods   总被引：3，自引：0，他引：3  

Joachim Hhle  Michael Hhle 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(4):398-406

Measures for the accuracy assessment of Digital Elevation Models (DEMs) are discussed and characteristics of DEMs derived from laser scanning and automated photogrammetry are presented. Such DEMs are very dense and relatively accurate in open terrain. Built-up and wooded areas, however, need automated filtering and classification in order to generate terrain (bare earth) data when Digital Terrain Models (DTMs) have to be produced. Automated processing of the raw data is not always successful. Systematic errors and many outliers at both methods (laser scanning and digital photogrammetry) may therefore be present in the data sets. We discuss requirements for the reference data with respect to accuracy and propose robust statistical methods as accuracy measures. Their use is illustrated by application at four practical examples. It is concluded that measures such as median, normalized median absolute deviation, and sample quantiles should be used in the accuracy assessment of such DEMs. Furthermore, the question is discussed how large a sample size is needed in order to obtain sufficiently precise estimates of the new accuracy measures and relevant formulae are presented.  相似文献   

Simulations of multimode bolometric interferometers     

George Saklatvala  Michael P. Hobson  Stafford Withington 《Monthly notices of the Royal Astronomical Society》2006,367(3):1194-1200

We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers.  相似文献   

Comet Hale-Bopp (C/1995 O1): UVSTAR-FUV Spectroscopy from the Space Shuttle     

Cristiano B. Cosmovici  Vojko Bratina  Gottfried Schwarz  Gianpaolo Tozzi  Michael J. Mumma  Roberto Stalio 《Astrophysics and Space Science》2006,301(1-4):135-143

We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 Å) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 Å) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N₂ are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 10²⁹ molecules s^?1 could be derived and compared with other post-perihelion observations.  相似文献   

The efficiency of the spiral-in of a black hole to the Galactic Centre     

Piero F. Spinnato  Michael Fellhauer  Simon F. Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2003,344(1):22-32

We study the efficiency at which a black hole or dense star cluster spirals in to the Galactic Centre. This process takes place on a dynamical friction time-scale, which depends on the value of the Coulomb logarithm (ln Λ). We determine the accurate value of this parameter using the direct N -body method, a tree algorithm and a particle-mesh technique with up to two million plus one particles. The three different techniques are in excellent agreement. Our measurement for the Coulomb logarithm appears to be independent of the number of particles. We conclude that  ln Λ= 6.6 ± 0.6  for a massive point particle in the inner few parsec of the Galactic bulge. For an extended object, such as a dense star cluster, ln Λ is smaller, with a value of the logarithm argument Λ inversely proportional to the object size.  相似文献   

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables – IV. Observations of frequency doubling and tripling in VW Hyi     

Brian Warner  Patrick A. Woudt 《Monthly notices of the Royal Astronomical Society》2006,367(4):1562-1576

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase, the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail, the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ∼100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the 'longer-period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400–1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to the transition from viewing a single accretion region to viewing two regions, and the rate of accretion on to the primary is modulated at the frequency of the 1st harmonic, as in the 'beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.  相似文献   

Translating Milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion: a conceptual link     

Michael Schulz  Christian Schäfer-Neth 《地学学报》1997,9(5-6):228-231

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Imaging the surface of Mercury using ground-based telescopes     

Michael Mendillo  Johan Warell  Sanjay S. Limaye  Jeffrey Baumgardner  Ann Sprague  Jody K. Wilson 《Planetary and Space Science》2001,49(14-15)

We describe and compare two methods of short-exposure, high-definition ground-based imaging of the planet Mercury. Two teams have recorded images of Mercury on different dates, from different locations, and with different observational and data reduction techniques. Both groups have achieved spatial resolutions of <250 km, and the same albedo features and contrast levels appear where the two datasets overlap (longitudes 270–360°). Dark albedo regions appear as mare and correlate well with smooth terrain radar signatures. Bright albedo features agree optically, but less well with radar data. Such confirmations of state-of-the-art optical techniques introduce a new era of ground-based exploration of Mercury's surface and its atmosphere. They offer opportunities for synergistic, cooperative observations before and during the upcoming Messenger and BepiColombo missions to Mercury.  相似文献   

2001 Leonard Medal Citation for Harry Y. McSween,Jr.     

Michael J. Drake 《Meteoritics & planetary science》2002,37(1):5-6

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